This invention relates to a brake adjuster for a heavy duty vehicle brake, and more particularly, the invention relates to a brake adjuster especially adapted for use with the pistons commonly found in heavy duty vehicle brakes.
Disc brake assemblies typically include a disc brake caliper that houses a piston for forcing a pair of friction elements or brake pads into engagement with a rotor. As the brake pads wear, the piston must move further to force the brake pads into engagement with the rotor. Accordingly, it is desirable to incorporate a wear adjustment mechanism to take up any clearance in the brake assembly as the brake pads wear. If a brake adjustment mechanism is not used, the vehicle operator will undesirably be required to push the brake pedal an additional amount to compensate for the wear in the brake pads and may also need to provide a greater force at the brake pedal.
Passenger vehicles typically use hydraulic brake cylinders that actuate a single hydraulic piston at each brake caliper. Because passenger vehicles have a relatively low vehicle weight the brake assemblies and brake adjustment mechanisms are relatively simple. Heavy duty vehicle brake assemblies commonly include multiple pistons that are actuated by a cam that is manipulated by a pneumatic actuator. The heavy duty brake assemblies are relatively complicated compared to passenger vehicle brake assemblies. Heavy duty brake assemblies have typically incorporated mechanical brake adjusters to adjust the pistons as the brake pads wear. Prior art non-mechanical brake adjusters are unsuitable for heavy duty vehicle brake applications. Therefore, it is desirable to develop a non-mechanical brake adjuster suitable for the pistons commonly used in heavy duty vehicle brakes.
The present invention provides a brake adjuster for a vehicle brake such as for heavy duty vehicle. The brake adjuster includes a brake module that produces an electrical signal for adjusting the vehicle brake. The heavy duty vehicle brake typically includes a pair of pistons each having first and second portions that are movable relative to one another. A friction element or brake pad is arranged proximate to the second portion and is movable from a desired position to a worn position as the brake pads wear during operation of the vehicle. In one embodiment of the present invention, the first and second portions are slip fit within a sleeve assembly. At least one adjustment member is arranged between the first and second portions. The adjustment member is constructed from a material which expands in response to an electrical signal, such as a magnetostrictive or a piezoelectric material. The adjustment member moves the second portion relative to the first portion and repositions the brake pads from the worn position to the desired position.
In another embodiment of the present invention, the first and second portions are threaded to one another and movable rotationally relative to one another to adjust the length of the piston. The first portions of the pistons include a plurality of teeth about the outer face. A gear is arranged between the pistons and coupled the teeth of the first portions together. An electric actuator has a driven member that is coupled with at least a portion of one of the pistons teeth to rotate the first and second portions relative to one another to increase the length of the piston. In this manner, the electric actuator moves the brake pad from the worn position to the desired position.
Accordingly, the above embodiments of the present invention provide a brake adjuster suitable for the pistons commonly used in heavy duty vehicle brakes